This invention relates to an improved prevailing torque-type lock nut, and a method and apparatus for forming such a nut.
Metal prevailing torque-type lock nuts are generally well known. Conventionally, these nuts are formed with a locking area wherein the internal threads are upset or deformed to create a binding action with the stud or bolt upon assembly to preclude the likelihood of the nut working loose in use. Such prevailing torque-type lock nuts are normally formed by deforming the outer portion of the upper end of the nut radially inwardly so that the threads will be displaced in this area. Although numerous lock nut designs exist wherein the outer portion of the nut is deformed at three equally spaced locations around the periphery of the nut, it is generally recognized that a lock nut which is distorted on only two radially opposed sides thereof exhibits superior torque retention characteristics due to the greater resiliency of the nut body. Examples of such lock nuts are shown in U.S. Pat. No. 3,198,230 entitled Lock Nut issued Aug. 3, 1965, in the name of J. H. Stover III and in U.S. Pat. No. 3,455,361 entitled Torque Nut issued July 15, 1969, to D. R. Zimmer et al.
However, lock nuts with two-sided distortion have several disadvantages. For example, the localized deformation of the locking portion of the nut has a tendency to distort the shape of the hex unless the nut is held within a die or collet during deformation. Thus, tolerances must be quite closely held with such nuts so that when the locking operation is performed on them, they will not be deformed outside of the normal specification range for the nut. This must be done to insure that standard tools may be used with the finished nut. Furthermore, the amount of deformation will be dependent upon the initial size of the nut. Normal tolerances with such elements will cause wide variations in the actual torque locking characteristics of the finished nut. As a result, the tolerances on the nut prior to the formation of the locking surface thereon must also be quite closely held. In addition to the aforenoted defects, all of which go to the cost, the prior art type of prevailing torque lock nuts have had a tendency to abraid the cooperating fastener when put in place and have a tendency to substantially reduce their locking chacteristics each time they are assembled and disassembled due to the manner in which they are formed. Furthermore, it has been necessary with the prior art type of lock nuts to accurately control the pressure applied to the nut when the locking formations are being made so as to more accurately control the torque characteristics of the finished product.
It is, therefore, a principal object of this invention to provide an improved torque-type lock nut and method and apparatus for making such a lock nut.
It is another object of the invention to provide a prevailing torque-type lock nut that offers more accurate control over its torque locking characteristics.
It is a further object of this invention to provide an improved low cost prevailing torque-type lock nut and method and apparatus of making it which permits wider tolerances while controlling the torque characteristics.
It is yet a further object of this invention to provide an improved prevailing torque-type lock nut and method and apparatus of making it which permits a greater number of reuses without adversely affecting the torque locking characteristics of the nut.